Mode hybridization phenomenon in air-cladded X-cut Y-propagating and Z-propagating thin film lithium niobate strip multimode waveguides is numerically studied and a mathematical relation between structural parameters leading to hybrid modes is formulated. Dependence of hybrid modes on waveguide dimensions, sidewall angles and wavelength is also analyzed. The results obtained are used to design lithium niobate on insulator (LNOI) taper for converting fundamental TM mode to higher order TE mode, and an optimum length for achieving a high conversion efficiency of 99.5% is evaluated. Birefringent Y-propagating LN and isotropic Z-propagating LN tapers are compared in terms of length, figures of merit, and fabrication tolerance. Tapers exhibit a broad bandwidth of 200 nm with an extinction ratio less than − 18 dB. The results of mode hybridization analysis are useful in design optimization of adiabatic tapers, tunable time delays, optical interconnects, mode converters and demultiplexers for mode division multiplexing (MDM) applications.
We report a large group velocity dispersion of hybrid modes in a LiNbO3-oninsulator multimode rib waveguide. A peak dispersion of ±49000 ps/(nm.km) is obtained in the mode hybridization region between TE 00 and TM 10 modes with a full width at half maximum of 10 nm. Dispersion for hybrid modes is tunable around ±15000 ps/(nm.km), ±22000 ps/(nm.km), and ±49000 ps/(nm.km) occurring at wavelengths of 1272, 1372, and 1496 nm, respectively, in the telecommunication band. In the wavelength range from 1530 to 1600 nm, the proposed rib waveguide is free of hybrid modes. In this region, the waveguide exhibits a flat dispersion profile for all eight guided modes with a maximum <1000 ps/(nm.km).
This paper presents theoretical analysis of a silicon based micro-machined differential pressure sensor using a square shaped clamped diaphragm and surface relief waveguide Bragg gratings embedded in a Mach Zehnder interferometer (MZI). Each of the arms of the MZI has one surface relief Bragg grating embedded in it. Each grating is mounted at the edge of a micro-machined diaphragm so as to obtain maximum stress. Coupled mode theory has been used to design the directional coupler to equally couple the light into both of the arms of MZI and also to design and analyse the shifts in the wavelengths of the Bragg gratings due to applied pressures. The wavelength shift difference of the two gratings gives the differential pressure sensitivity and also eliminates the noise due to temperature variation. Simulation results indicate that the differential pressure measurement sensitivity is 0.2 pm/Pa.
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